Exodus 12:29, 33, 42, 51

Now it happened at midnight that the LORD struck every firstborn in the land of Egypt, from the firstborn of Pharaoh who sat on his throne to the firstborn of the prisoner who was in the dungeon, and all the firstborn of the cattle.

The Egyptians [anxiously] urged the people [to leave], to send them out of the land quickly, for they said, “We will all be dead.”

It is a night of watching to be observed for the LORD for having brought them out of the land of Egypt; this [same] night is for the LORD, to be observed and celebrated by all the Israelites throughout their generations.

And on that very same day the LORD brought the Israelites out of the land of Egypt by their hosts (tribal armies).